The present invention relates to a traffic light signal control which can change the normal traffic mode of operation of the signal to an emergency mode of operation in response to a command from an emergency vehicle.
It is well known that emergency vehicles, such as fire engines, police vehicles and medical vehicles, utilize an audible signal to control traffic in the direction in which they are traveling. For a variety of reasons there have occurred accidents at intersections since drivers of regular vehicles have failed to respond to the audible and visual signals that are emitted by the emergency vehicle. In the past there have been several proposals for controlling intersections directly from emergency vehicles as, for example, the systems disclosed in Long U.S. Pat. No. 3,550,078 and Coll et al U.S. Pat. No. 3,638,179. In each of these prior art systems the traffic light at each intersection is equipped with a receiving means. For example, the Long patent provides a light beam that is pulsed which is received by the device for controlling the traffic light and the Coll et al patent discloses the system wherein radio signals that are omnidirectional are received by the traffic light controller which radio signals are coded for direction. Systems of this latter type require that the operator know the direction in which he is travelling and can under some circumstances cause confusion and the ability of having the wrong signal transmitted by accident without proper control being initiated at the intersection as desired by the vehicle. The Long patent, on the other hand, utilizes directional control, that is to say four detectors facing in four different directions and the transmitter on the vehicle effectively receives a train of pulses which are then integrated over a finite period of time. It is specifically suggested that ten pulses per second transmitted and that in a two-second period the desired threshhold voltage is reached by the integrating circuit so as to obtain the necessary control. It can be recognized that under some conditions this time span is too long and as a result the circuit can under some circumstances be incapable of acquiring traffic signal control. In addition there is no provision for rejection of false or spurious signals. Further neither of the above mentioned patents provide for the sending of various and different coded words to selectively operate the traffic signals or to provide any other function.